Allelic inactivation of rDNA loci

Sharon Schlesinger, Sara Selig, Yehudit Bergman, Howard Cedar*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


Human cells contain several hundred ribosomal genes (rDNA) that are clustered into nucleolar organizer regions (NORs) on the short arms of five different acrocentric chromosomes. Only ∼50% of the gene copies are actually expressed in somatic cells. Here, we used a new cytological technique to demonstrate that rDNA is regulated allelically in a regional manner, with one parental copy of each NOR being repressed in any individual cell. This process is similar to that of X-chromosome inactivation in females. Early in development, one copy of each NOR becomes late-replicating, thus probably marking it for inactivation and subsequent targeted de novo methylation at rDNA promoter regions. Once established, this multichromosomal allelic pattern is then maintained clonally in somatic cells. This pathway may serve as an epigenetic mechanism for controlling the number of available rDNA copies during development.

Original languageAmerican English
Pages (from-to)2437-2447
Number of pages11
JournalGenes and Development
Issue number20
StatePublished - 15 Oct 2009


  • DNA methylation
  • Early development
  • Monoallelic expression
  • Replication timing
  • Ribosomal DNA


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